This invention relates to a dual containment pipe system for installation within an existing conduit, and more particularly to a dual containment pipe system which provides a uniform space between a new primary containment pipe and the existing conduit, or between the new primary containment pipe and a new secondary containment pipe if the existing conduit is in need of repair. The newly created space between the pipes is suitable for receiving a leak detection system.
There is continuing need to provide pipes and methods of installation for rehabilitating existing pipelines. Due to the fact that many existing conduits handle hazardous liquids, chemicals and petroleum products, and that such pipelines are often located underground, it is desirable to install leak detection systems to meet new environmental regulations and assure health and safety of present and future generations. In these situations it is preferable to be able to rehabilitate and retrofit existing conduits without having to excavate. One such two-wall leakage detection system for an existing conduit is disclosed in U.S. Pat. No. 5,172,730, which issued on Dec. 22, 1992 to one of the inventors herein, the contents of which are incorporated herein by reference.
While this existing two-wall pipe and leakage detection system is fully satisfactory, it utilizes a soft absorbent or felt-type material to form the annular space. One advantage is that it is suitable for retrofitting relatively long lengths of existing pipe. An alternative construction of a pipeline monitoring leak containment system is illustrated in U.S. Pat. No. 5,072,622 issued on Dec. 17, 1991 to Roach et al. The pipe system disclosed by Roach et al. includes a pipe having an exterior wall in tight engagement with the interior wall of the carrier pipe with at least one groove located in the exterior surface of the containment pipe. The groove and the interior wall of the outer carrier pipe define at least one passageway. While it is believed that this system is suitable for relatively short lengths, it is limiting in that the containment pipe need be of the substantially rigid type and tends to be expensive to form such grooves on a wide variety of pipes of different sizes. An advantage of this system is that the space formed in the groove should remain uniform along the length of the groove.
A well-known process for rehabilitation of existing conduits generally utilizing a flexible liner to be cured in place is the "Insituform.RTM." method described in U.S. Pat. Nos. 4,009,063 and 4,064,211, the contents of which are incorporated herein by reference. Another rehabilitation process known as the "NuPipe.RTM." process described in U.S. Pat. Nos. 4,867,921 and 5,255,624, the contents of which are incorporated here by reference. In this latter process a substantially rigid replacement pipe is installed in a flattened and folded shape, heated and expanded to the shape of the original conduit.
In the Insituform.RTM. method, the lining tube is everted into the existing conduit from one end, the lining tube being provided on its outer side with an impermeable coating or film which after eversion becomes the inner surface of the pipeline providing a smooth flow enhancing surface to the interior of the relined pipeline or passageway. While the Insituform.RTM. process is extremely viable for relining long lengths of existing conduits, it would not be suitable to provide grooves on the outer surface of such a liner if a dual containment configuration were desired. A separate body of absorbent material may be provided as in U.S. Pat. No. 5,172,730, identified above.
Accordingly, it is desirable to provide an improved dual containment pipe which is not limited to liners which are rigid or flexible prior to installation, and which will provide a substantially uniform annular space along the full length of the pipeline when installed.